Dryptosaurus was fairly large, maybe 7m, and I
assume hadrosaurs were the principal prey for any top
predator in the east. There apparently were no large
ceratopsids or sauropods.

That still doesn't mean "the same ecological niche". Different predator
species with the same prey but different hunting methods, and/or different
hunting times (day/night...), can often coexist. Especially if they don't
have quite the same habitats.